For several years it has been common practice to form air distribution ducts from panels of self-supporting rigid thermal insulation of the mineral fiber type. These panels may be formed by, for example, a four by eight foot sheet of insulating material to one surface of which is adhered a kraft paper layer on which has been deposited a thin layer of aluminum. The metal foil outer surface thus provided may be reinforced by an imbedded netting of cords or "skrim". Heretofore these panels of duct wall have been grooved longitudinally at the job site and the duct section formed by folding the panel into a tube with the longitudinal seam being established and sealed by adhesive, preferably metallic tape running the length of the duct section. In such application the tape eventually dries out and peels from the duct wall and maintaining a sealed seam in the duct is difficult.
The concept of the present invention involves modifying conventional duct board panels by adding to it metal framing strips, on which suitable locking or joining configurations have been preformed. By proper scoring or grooving of the modified sheets they may be conveniently formed into the desired duct work configuration at the installation site but may be transported to the site in flat, unformed condition. The metal framing strips applied to the panels add to its rigidity and strength in transport and after assembly. The longitudinal locking seam, made possible by the presence of the adjacent metal framing strips when the panel has been formed into a duct section, makes the use of sealing tape unnecessary along the longitudinal seam and at the junction between duct sections. Labor saving in the installation of the duct wall board of the present invention over conventional assembly methods is substantial. While described herein with respect to forming of rectangular duct sections it will be understood that the panels of the present invention might also be used to form various air distribution fittings such as duct angles, elbows, reducers and the like.